Method for producing a dinitronaphthalene-isomer mixture having a high 1,5-dinitronaphthalene proportion

ABSTRACT

A process for producing a mixture of isomers of dinitronaphthalene by nitration of nitronaphthalene, in which nitronaphthalene, optionally in an inert organic solvent, is reacted with 1 to 20 times the equivalent quantity, based on the quantity of nitronaphthalene, of 50% to 100% nitric acid in the presence of a solid, perfluorinated, strongly acidic ion exchanger.

This invention relates to the production of a mixture of isomers ofdinitronaphthalene containing an increased proportion of1,5-dinitronaphthalene (referred to below as 1,5-DNN) by the nitrationof pure 1-nitronaphthalene or of a crude nitronaphthalene mixture.1,5-Dinitronaphthalene is a key compound for the production of1,5-diaminonaphthalene (referred to below as 1,5-NDA). This is, interalia, the starting compound for the production of1,5-diisocyanatonaphthalene (1,5-NDI, trade name Desmodur 15®). 1,5-NDIis used as the isocyanate component in polyurethanes.

The production of nitrated aromatics has been known for a long time (G.A. Olah et al., Nitration: Methods and Mechanisms, VCH, New York, 1989).For decades, corresponding nitroaromatics have been producedindustrially by nitration using a mixture of sulfuric acid and nitricacid (so-called mixed acid or nitrating acid). Nowadays polynitrations,for example dinitrations, are mostly carried out on the large scale by atwo-step nitration (Kirk-Othmer, Encyclopedia of Chemical Technology,1981, Vol. 15 and Ullmann, Encyclopedia of Industrial Chemistry, 1991,Vol. A17, pages 411-455).

The nitration of naphthalene (Houben-Weyl, Methoden der OrganischenChemie, 1971, Vol. 10, pages 492-495) yields a mixture of the isomers1-nitronaphthalene and 2-nitronaphthalene in the ratio of about 95:5. Inthe nitration of the isomerically pure 1-nitronaphthalene using amixture of sulfuric acid and nitric acid, a mixture of 1,5- and1,8-dinitronaphthalene in the ratio of about 1:2 is formed, in additionto about 5% of other isomers (for example, 1,6- and 1,7-DNN). Theunfavourable selectivity of the reaction leads in the production of1,5-DNN chiefly to a high and undesirable content of 1,8-DNN.

DE-A 11 50 965 reports the increase in the selectivity by a rapid andintensive mixing of 1-nitronaphthalene dissolved in sulfuric acidtogether with nitrating acid. A disadvantage of this process is theconsiderable quantity of sulfuric acid used as solvent, the working-upof which is very expensive and cost-intensive. In addition, considerablequantities of trinitrated products, which both significantly decreasethe yield of 1,5-DNN and are to be considered critical as regards safetyregulations, can be formed in this process—particularly in the adiabaticreaction procedure described in the above-mentioned prior art.

WO 94/19310 describes nitrations of nitroaromatics on aluminiumsilicates partially doped with heavy metal, so-called claycops, as solidcatalyst, which deliver high yields of dinitrated products together withsmall quantities of trinitroaromatics. However, nitrations of1-nitronaphthalene carried out by this process yield ratios of isomerssimilar to those in classical nitrations with mixed acid.

Nitrations with nitric acid in organic solvents, for example,dichloroethane, and azeotropic removal of the water of the reaction aredescribed in DE-A 24 53 529. They deliver dinitronaphthalene in highyields, but without influencing the ratio of isomers.

The object, accordingly, was to find a process for producing a mixtureof isomers of dinitronaphthalene containing a high proportion of1,5-dinitronaphthalene by nitration of 1-nitronaphthalene, in whichmixed or nitrating acid, which simply entails expensive working up, neednot be used.

Surprisingly, it has now been found that a shift of the ratio of isomerstowards 1,5-DNN is possible where solid, perfluorinated, strongly acidicion exchangers are used as catalyst in the nitration of1-nitronaphthalene. The reaction is carried out in an excess of nitricacid, which can be recovered on completion of the reaction and afterconcentration.

The invention therefore provides a process for producing a mixture ofisomers of dinitronaphthalene by nitration of nitronaphthalene, whereinnitronaphthalene, optionally in an inert organic solvent, is reactedwith 1 to 20 times the equivalent quantity, based on nitronaphthalene,of 50% to 100% nitric acid in the presence of a solid, perfluorinated,strongly acidic ion exchanger. 1 to 20 times the equivalent quantitycorresponds, in the case e.g. of a 65% nitric acid, to 33 wt. % to 92wt. %, based on the solution, and in the case of an 100% nitric acid, to26 wt. % to 88 wt. %.

The mixtures of DNN isomers produced according to the invention containa surprisingly high proportion of the 1,5-DNN isomer. Conventionally,the content of 1,5-DNN is more than 30 wt. %, in particular between 34and 50 wt. %. The content of other secondary products, in particular ofother isomers of dinitronaphthalene and of more highly nitratedproducts, is smaller than in comparable nitrations with mixed acid.

The starting product used can be pure 1-nitronaphthalene or even a crudenitronaphthalene mixture, such as is obtained as crude product in thenitration of naphthalene.

The solid, perfluorinated, strongly acidic ion exchanger catalyses thereaction to form the 1,5-dinitronaphthalene-enriched end product. Suchperfluorinated, strongly acidic ion exchangers are known in prior artand are commercially available, for example, under the trade nameNafion®. Preferably an ion-exchange resin with the trade name Nafion® NR50 Superacid Catalyst (Dupont) is used.

The ion exchanger used as catalyst is chemically inert and can be easilyremoved from the reaction batch, for example, by filtration. A workingup, as in the case of the diluted and organically contaminated sulfuricacid which accumulates during nitrations with mixed acid (nitricacid/sulfuric acid mixture), is advantageously omitted in the processaccording to the invention.

The concentration of the nitric acid is between 50% and 100%, preferablybetween 60% and 80%. The quantity of nitric acid added is between 1equivalent and 20 equivalents, based on the quantity of nitronaphthaleneused. In the case of a 65% nitric acid, this corresponds to 33 to 92 wt.%. Preferably quantities of nitric acid of between 3 equivalents (in thecase of 65% nitric acid: 62.7 wt. %) and 12 equivalents (correspondingto 87.0 wt. % of 65% nitric acid) are used.

The process is conventionally carried out at temperatures of between 20°C. and 100° C., preferably 80° C.

To ensure a complete reaction, the conversion is carried out withthorough mixing of the reaction mixture, for example, by intensivestirring for a reaction period of between 20 minutes and 8 hours, forexample, 3 hours.

In the absence of additional solvent, the process according to theinvention can only be carried out in an excess of nitric acid, or elseoptionally after the introduction of a solvent.

In this connection, the 1,5-selectivity can, surprisingly, be increasedeven further in the presence of an inert organic solvent.

The process according to the invention is therefore preferably carriedout in the presence of an inert organic solvent. Suitable solvents ofthis kind are polar compounds which are inert in the reaction medium.Examples of such solvents are sulfolane or nitroalkanes, such as, forexample, nitromethane.

The process according to the invention is preferably carried out in thepresence of sulfolane as organic solvent.

Unreacted nitronaphthalene, excess nitric acid and solvent can bereturned to the process.

The quantity of organic solvent added is between 0.1 and 20 parts andpreferably between 0.5 and 3 parts, based on the quantity ofnitronaphthalene used. The concentration of the nitric acid is adjustedaccording to the quantity of solvent added and is between 50% and 100%,preferably 60% to 80%.

The mixture of isomers of dinitronaphthalene can be separated into theisomeric dinitronaphthalenes in known manner, for example, by fractionalcrystallisation. Such separations of isomers, for example, withdimethylformamide or dichloroethane as solvent, have already beendescribed (cf. Houben-Weyl, Methoden der organischen Chemie, 1971, Vol.10, page 494).

The invention also provides mixtures of isomers consisting of 1,5- and1,8-dinitronaphthalene, having a 1,5-dinitronaphthalene content of morethan 30 wt. %, in particular of between 34 and 50 wt. %.

These mixtures of isomers of dinitronaphthalene are preferably obtainedby the process according to the invention described above.

The 1,5-DNN can be separated from the mixture of isomers according tothe invention in known manner and used for the production of 1,5-NDA and1,5-NDI. The following Examples are intended to explain the invention,without thereby limiting its scope.

EXAMPLES

Pure 1-nitronaphthalene was used as the starting material.

The ion exchanger used as catalyst, with the trade name Nafion® NR 50Superacid Catalyst (Dupont), in the Examples below is referred to simplyas Nafion.

1. Nitration of 1-nitronaphthalene Using Nitric Acid with Nafion asCatalyst

1.1 Nitration with Nafion-H and 0.6 mol Nitric Acid

10 g Nafion and 17.3 g (0.1 mol) 1-nitronaphthalene were added to 58.2 gof 65% (w/w) nitric acid (corresponding to 0.6 mol). The batch was thenstirred for 3 hours at 80° C. Working up was carried out by introducingthe reaction batch into 1000 ml ice water, filtering off andsubsequently drying the solid substance. The dinitronaphthalene wasseparated from the catalyst by extraction with dioxane. Here the solidsubstance was placed in 200 ml dioxane at 90° C. and stirred for 30minutes, then the catalyst was filtered off and the dioxane was removedby distillation.

The isomeric composition of the residue was determined by gaschromatography (HP 5890, column: 25 m SE 30, injector: 300° C., detector(FID): 320° C., temperature programme: Start: 100° C., heating rate: 10°C./min, end temperature: 320° C., quantity of sample: 2% in dioxane,quantity injected: 1 μl).

1.2 Nitration with Nafion-H and 8 mol Nitric Acid

10 g Nafion and 17.3 g (0.1 mol) 1-nitronaphthalene were added to 77.6 gof 65% (w/w) nitric acid (corresponding to 0.8 mol). The batch was thenstirred for 3 hours at 80° C. The working up and determination of theisomeric composition were carried out as in 1.1.

1.3 Nitration without Nafion-H and 6 mol Nitric Acid (ComparisonExample)

17.3 g (0.1 mol) 1-nitronaphthalene was added to 58.2 g of 65% (w/w)nitric acid (corresponding to 0.6 mol). No Nafion was added. The batchwas then stirred for 3 hours at 80° C. Working up was carried out byintroducing the reaction batch into 1000 ml ice water and filtering offthe solid substance. The determination of the isomeric composition wascarried out as in 1.1.

1.4 Nitration with H₂SO₄ and 6 mol Nitric Acid (Comparison Example)

17.3 g (0.1 mol) 1-nitronaphthalene was added to 58.2 g of 65% (w/w)nitric acid (corresponding to 0.6 mol) and 10.0 g sulfuric acid (0.1mol). The batch was then stirred for 3 hours at 80° C. Working up wascarried out by introducing the reaction batch into 1000 ml ice water andfiltering off the solid substance. The determination of the isomericcomposition was carried out as in 1.1.

The experimentally determined isomeric compositions are given inTable 1. In nitrations with Nafion, there is a higher 1,5-yield and animproved ratio of (1.5)/(1.8)-DNN. This is in accordance with acorresponding increase in the 1,5-selectivity in the nitration.

TABLE 1 Composition of the product mixture in the nitration of 1-nitronaphthalene with nitric acid (Examples 1.1 to 1.4); the equivalentsof the nitrating agent, the concentration of the nitric acid used andthe reaction temperature are shown. The composition of the productmixture (in per cent) was determined by gas chromatography. Theproportion of 1-nitronaphthalene (1-MNN), 1,5- dinitronaphthalene(1,5-DNN), 1,8-dinitronaphthalene (1,8-DNN) and the sum of theproportions of other DNN-isomers and trinitronaphthalene (DNN + TNN) areshown, as well as the ratio of the products 1,5-DNN and 1,8-DNN$\left( \frac{1,{5 - {DNN}}}{1,{8 - {DNN}}} \right)$

formed. Ex. HNO₃ Catalyst solvent 1-MNN 1,5-DNN 1,8-DNN$\frac{1,{5 - {DNN}}}{1,{8 - {DNN}}}$

Σ of other DNN & TNN 1.1 6 × 65%, Naflon 22.1 34.1 38.0 0.90 5.8 80° C.1.2 6 × 65%, Naflon 2.7 43.5 49.3 0.88 4.5 80° C. 1.3 8 × 65%, — 33.822.5 36.3 0.62 7.4 80° C. 1.4 6 × 65%, H₂SO₄ 0.1 29.6 57.3 0.52 13.0 80°C.

2. Nitration of 1-nitronaphthalene Using Nitric Acid with Nafion asCatalyst in the Presence of an Organic Solvent

2.1 Nitration with Nafion-H and 0.6 mol Nitric Acid in the Presence ofSulfolane

10 g Nafion, 30 g sulfolane and 17.3 g (0.1 mol) 1-nitronaphthalene wereadded to 58.2 g of 65% (w/w) nitric acid (corresponding to 0.6 mol). Thebatch was then stirred for 3 hours at 100° C. The working up anddetermination of the isomeric composition were carried out as in 1.1.

2.2 Nitration with Nafion-H and 0.6 mol Nitric Acid in the Presence ofNitromethane

10 g Nafion, 30 g nitromethane and 17.3 g (0.1 mol) 1-nitronaphthalenewere added to 58.2 g of 65% (w/w) nitric acid (corresponding to 0.6mol). The batch was then stirred for 3 hours at 100° C. The working upand determination of the isomeric composition were carried out as in1.1.

The experimentally determined isomeric compositions are given in Table2. The addition of the solvent results in higher ratios of(1.5)/(1.8)-DNN. This is in accordance with a corresponding increase inthe 1,5-selectivity in the nitration.

TABLE 2 Composition of the product mixture in the nitration of 1-nitronaphthalene with nitric acid and addition of a solvent (Examples2.1 to 2.2); the equivalents of the nitrating agent, the concentrationof the nitric acid used and the reaction temperature are shown. Thecomposition of the product mixture (in per cent) was determined by gaschromatography. Catalyst/ Ex. HNO₃ solvent 1-MNN 1,5-DNN 1,8-DNN$\frac{1,{5 - {DNN}}}{1,{8 - {DNN}}}$

Σ of other DNN & TNN 2.1 6 × 65%, Naflon/ 68.9 15.0 9.1 1.65 7.0 100° C.sulfolane 2.2 8 × 65%, Naflon/ 55.6 18.7 17.9 1.04 7.8 100° C. nitro-methane

What is claimed is:
 1. A process for the production of an isomericmixture of dinitronaphthalene comprising reacting a) nitronaphthalenewith b) nitric acid having a concentration of from 50 to 100% in anamount that is from 1 to 20 times the equivalent amount of a) in thepresence of c) a solid, perfluorinated, strongly acidic ion exchanger.2. The process of claim 1 in which an inert organic solvent is presentin a).
 3. The process of claim 1 in which a) is a crude nitronaphthalenemixture.
 4. The process of claim 2 in which the inert organic solvent isa nitroalkane and/or a sulfolane.
 5. The process of claim 4 in which theinert organic solvent is used in an amount of from 0.1 to about 20 partsby weight, based on the weight a).
 6. An isomeric mixture ofdinitronaphthalene in which from about 45 to about 60% by weight is1,8-dinitronaphthalene and from about 35 to about 50% by weight is1,5-dinitronaphthalene and in which the ratio of 1,5-dinitronaphthaleneto 1,8-dinitronaphthalene is at least 0.88.
 7. The isomeric mixture ofclaim 6 which has been produced by reacting a) nitronaphthalene with b)nitric acid having a concentration of from 50 to 100% and an amount offrom 1 to 20 times the equivalent amount of a) in the presence of c) asolid, perfluorinated, strongly acidic ion exchanger.